The present invention relates to a disc brake of a motor vehicle and to a brake lining.
Generic disk brakes are composed substantially of a brake disc which rotates with a vehicle axle during operation, at least one or more brake linings arranged at one side or preferably at both sides of the brake disc, a brake caliper, and preferably a brake carrier which extends to one or both sides of the brake disc. The disc brake which has the brake carrier preferably has a sliding caliper which is movable relative to the brake carrier, or a pivoting caliper.
To ensure reliable functioning of the disc brake, it is necessary for the brake linings to be reliably guided and supported in the brake caliper or the brake carrier.
The generic known brake carrier (and thus also the brake carrier according to the invention) has for this purpose preferably on each side of the brake disc preferably two carrier lugs which are arranged one behind the other in the circumferential direction of the brake disc and which are connected to one another by at least one strut and which project radially from a frame and which laterally delimit a lining slot for receiving a brake lining. Here, according to the prior art, the lining slot is preferably furthermore formed so as to be open in the outward direction, such that the brake linings can be pushed into it radially from the outside. After being inserted, the brake linings are fixed radially by a hold-down bracket. A lining retention spring may optionally be provided, in particular one which is arranged and acts resiliently between the lining hold-down bracket and the brake lining.
The brake linings are subjected, during operation, to a multiplicity of loadings. The brake linings are subjected to high thermal loading and mechanical loading. Different loading states arise in the two operating states a) brake actuated and b) brake not actuated.
During an actuation of the brake, the brake lining is subjected to high pressure and transverse forces, wherein the brake lining has to perform the task of introducing transverse forces generated at the friction surface of the brake lining via the lining compound into a lining carrier plate, and from there into the brake caliper or the brake carrier. Here, the transverse forces acting on the brake lining are accommodated primarily by the exit-side carrier lug, that is to say the carrier lug situated at the front in the direction of travel of the brake disc.
Furthermore, the brake lining must convert the application force generated by the brake caliper into a pressure force which is distributed as uniformly as possible over the friction surface. For this purpose, the application force generated by the brake caliper must be converted into an areal load by the flexurally rigid lining carrier plate.
It is a problem that, owing to the limited installation space conditions, the frontal narrow sides or support surfaces of the lining carrier plate of the known brake lining which bear against the brake carrier cannot prevent a rotational movement of the brake lining during a braking process. Said rotational movement can have an adverse effect on the air play, that is to say the clearance between the friction lining and brake disc, and on the wear behaviour of the brake linings, in particular in the form of oblique wear and the clearance of the linings.
German patent publication no. DE 29 26 818 A1 is cited as prior art.
It is an object of the present invention to further develop a disk brake of the generic type in such a way that the above-described adverse effects on the operating behaviour can be substantially eliminated.
Here, the carrier lug which is situated at the rear in a main direction of rotation of the brake disc, that is to say the direction of rotation of the brake disc during forward travel of the motor vehicle, is referred to as the entry-side carrier lug.
Correspondingly, the carrier lug which is situated at the front in a main direction of rotation of the brake disc, that is to say the direction of rotation of the brake disc during forward travel of the motor vehicle is referred to as the exit-side carrier lug.
In this case, the exit-side carrier lug and the associated contour of the lining carrier plate have, in each case, at least in the region of the highest support point in the radial direction, a support surface which is inclined at an angle of inclination α>0° relative to the Y axis, wherein said support surfaces are designed for abutment against one another during braking processes in the main direction of travel.
To prevent the brake lining from sliding away tangentially owing to the oblique position of the highest support point A, the angle of inclination is in this case preferably smaller than the sum of a force introduction angle and the arc tangent of a friction value μa at the support point on the exit-side carrier lug. Angles of inclination α of between 8° and 30° have proven to be particularly advantageous. Also, for ensuring that the lining does not slide away tangentially on the support of the carrier lug, values of between at least 8° and at most 30° for the angle α preferably emerge.
In the disc brake according to the invention, in which the entry-side carrier lug of the brake carrier of the disc brake and the support surface, which is adjacent thereto, of the lining carrier plate engage into one another, the brake lining is supported on the exit-side carrier lug at a support point which lies below a force action line which represents the total friction force.
The force distribution on both carrier lugs which can be attained in this way has an advantageous effect on braking behaviour.
Firstly, the brake lining is subjected to a resulting defined torque about a Z axis parallel to the axis of rotation of the brake disk. As a result of said torque, a support force is advantageously exerted on the carrier lug at the entry side, too, and said side of the brake carrier is thus also incorporated into the force flow during a braking process, resulting in turn in a more expedient force distribution or introduction being attained in the brake carrier. By contrast, the case of conventional brake carriers without entry-side support of the brake lining, a very large proportion of the lining support takes place at the exit-side carrier lug.
Advantageous, then, is the force distribution on both carrier lugs, which is more uniform than in the prior art, during a braking process, which is also contributed to significantly by the relatively low highest support point (in the Y direction).
This shall be explained on the basis of a first model study. In simplified form, to describe a lining, it is possible to assume a model of a ring segment which is short in the circumferential direction (that is to say the coverage angle φ in the circumferential direction is assumed, in simplified form, to be relatively small), for which there is a resulting force action line or a force action vector through the centre of gravity of the brake lining in the X direction (perpendicular to the brake disc axis of rotation). In FIG. 2 et seq., said force action vector, in the variants illustrated in the figures, lies radially exactly or approximately in the centre of the brake lining. By contrast, the exit-side support on the brake carrier takes place—in this regard see also FIGS. 3 and 4 and the further appended illustrations aside from FIG. 1—preferably and advantageously further inward, in the Y direction perpendicular to the brake disc axis, relative to the force action vector applied to the centre of gravity. This also applies to the figures in which no brake carrier is illustrated.
The highest support point A of the brake lining on the exit-side carrier lug in the Y direction particularly preferably has a spacing h to the force action line, which spacing amounts to at least 0.1 times the length of the brake lining in the direction of the force action line of the total friction force and/or between 0.1 and 0.25 times the width of the brake lining perpendicular to the direction of the force action line of the total friction force. In this way, the force introduction distribution is advantageous at the entry side too, which will be explained in more detail further below, especially advantageous.
It is furthermore particularly advantageous, according to one refinement of claim 1 which is however also to be considered to be an independent invention, for the exit-side carrier lug and the associated contour of the lining carrier plate to have, in each case, a support surface which is inclined at an angle of inclination α>0° relative to the Y axis, wherein said support surfaces are designed for abutment against one another during braking processes in the main direction of travel.
To prevent the brake lining from sliding away tangentially owing to the oblique position of the highest support point A, the angle of inclination is in this case preferably smaller than the sum of a force introduction angle and the arc tangent of a friction value μa at the support point on the exit-side carrier lug. Angles of inclination α of between 8° and 30° have proven to be particularly advantageous. Also, for ensuring that the lining does not slide away tangentially on the support of the carrier lug, values of between at least 8° and at most 30° for the angle α preferably emerge.
The studies discussed above apply to braking processes in the forward direction. In order that braking processes in the reverse direction are however also possible without functional impairment, the brake carrier lug which is oriented toward the entry side in the forward direction must have a minimum height. An advantageous rule here is that the height of the brake carrier lug should be greater than the height position of the action line, oriented in the circumferential direction, of the lining friction forces. It is in this way ensured that no additional turning-out torque is exerted on the brake lining by the support of the brake lining.
In one advantageous design variant of the present invention—which may be considered firstly to be a refinement of the above subject matter but also secondly to be an independent invention—the exit-side carrier lug of the brake carrier is formed so as to be lower than the entry-side carrier lug of the brake carrier. This refers in particular to the radial distance to the axis of rotation (Z axis) of the brake disc. The entry-side carrier lug, which is formed so as to be radially elevated in relation to the exit-side carrier lug, ensures in particular reliable retention and prevention of the brake lining turning out of the brake carrier at the entry side.
In particular, the entry-side carrier lug is higher than a point of intersection of the force action line with the entry-side carrier lug, which improves the support of the brake lining even during reverse travel.
According to a further design variant, the outlet-side carrier lug of the brake carrier and the support surface, which is adjacent thereto, of the lining carrier plate are formed such that the lining carrier plate can pivot out of the brake carrier, radially away from the axis of rotation of the brake disc, at the exit side. In this way, while a structural design of the brake carrier and lining carrier plate is provided which prevents a rotational movement of the brake lining, simple installation and removal of the brake lining is simultaneously possible. Here, the installation and removal of the brake lining in the brake carrier may be performed in a simple manner by means of a pivoting movement.
According to one advantageous design variant, the support surface of the lining carrier plate which is adjacent to the entry-side carrier lug has an offset which engages into an undercut, which corresponds to the offset, on the entry-side carrier lug. In this way, the brake lining is prevented from turning out at the entry side not only by the presence of adequate friction forces but rather also by the shaping of the lining carrier plate and of the entry-side carrier lug, as a result of which the redistribution of relatively high support forces at the entry side is also made possible. Particularly advantageous here is a positively locking engagement of the offset into the undercut on the entry-side carrier lug, for example by virtue of the entry-side carrier lug having a head piece which engages over the offset on that support surface of the lining carrier plate which is adjacent to the entry-side carrier lug.
According to a further particularly preferred design variant, the lining carrier plate is, as a result of the design of the respective offsets, formed so as to be asymmetrical about a mirror axis which extends centrally through the brake lining and which runs through the axis of rotation of the brake disc. This, too, yields numerous advantages. As a result of the entry-side guidance, which acts in the radial direction, of the brake lining, a rotational effect of the brake lining during a braking process is prevented. Furthermore, as a result of the asymmetry, an asymmetric arrangement of the friction compound of the brake lining is possible, for example in order to compensate oblique wear of the friction compound. Furthermore, as a result of the asymmetrical design, incorrect installation of the brake lining into the brake carrier is practically ruled out. The undercut extends preferably as a projection in the direction of the main direction of rotation of the brake disc and is engaged under by the lining carrier plate at the entry side, such that the brake lining cannot be removed from the brake carrier directly radially relative to the brake disc central point.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.